Etchant

ABSTRACT

An etching treatment agent which can etch insulating film with high speeds without damaging the resist pattern, provide realistic throughput when the insulting film etching process in the semiconductor manufacturing process is replaced with the single wafer processing etching treatment method, and prevent roughness on the surface of the semiconductor after etching.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an etchant and more particularly, to anetching treatment agent used for fine treatment of insulating film suchas silicon oxide or the like at a high speed and uniformity in themanufacturing process of semiconductor devices.

2. Description of the Related Art

Cleaning, etching, and patterning of a wafer surface and afinely-manufactured surface with higher cleanliness, higher precision,and more advanced performance are becoming more important with thetendency for increasingly higher integration and higher capability ofintegrated circuits in the wet process of the manufacturing process forsemiconductor integrated circuits.

Both a solution of hydrogen fluoride (HF) and a mixed solution (bufferedhydrogen fluoride) of HF and ammonium fluoride (NH₄F) are applied forthe purpose of cleaning and patterning as a surface treatment agent forfine surface treatment, but in order to acquire submicron ultra highintegration, higher performance and higher capability is increasinglyrequired. Further, although the wafer currently averages 8 inches indiameter, it is predicted that the wafer will be 12 inches in diameterby the year 2000.

A wet etching method for a wafer in the conventional case is the batchmethod of putting 25 to 50 sheets of wafer into a cassette, soaking thewhole cassette into an etching bath, and subjecting the cassette toetching treatment. Further, a cassette-less type of cleansing method isemployed for preventing drag-in of a solution.

The batch method described above has the advantage of high throughputbecause of enabling concurrent etching onto a large number of wafers,but has the disadvantage of low uniformity of etching within eachsurface of the wafers. This low uniformity is more noticeable when thewafer size is larger, such as the 12 inch diameters predicted in thefuture, and it is conceivably difficult to obtain etching uniformitywithin the surface of a wafer in current batch processing. In addition,the difficulty will be more serious in accordance with increasedtolerance necessary in the art.

And for this reason, in order to enhance etching uniformity, a singlewafer processing type etching method in which an etching solution issupplied onto a wafer being rotated has been considered. This method hasthe advantage of enhancement of the uniformity, but has a disadvantagein that a long time is required for the some throughput as batchprocessing.

Namely, the buffered hydrogen fluoride solution (BHF) havingconventionally been applied is prepared for application usually bymixing 40 percent NH₄F and 50 percent HF in various mixing ratios (suchas in a range of 400:1 to 6:1), and etching speeds to silicon oxide filmby this BHF are in a range from 27 nm/min to 115 nm/min.

The time required for etching onto 50 sheets of wafer each with oxidefilm having a thickness of 500 nm in the batch method, with BHF obtainedby mixing HF and NH₄F in a ratio, for example, 7:1 is about 5 minutes.But, if the treatment is carried out by the cut sheet type of methodwith this BHF, the treatment for only one sheet thereof requires about 5minutes, and so it is understood that the treatment for 50 sheetsthereof requires the time 50 times as much as that by the batch method,namely 250 minutes.

Such an enormous time is unrealistic for a line of mass productionfacilities, and in order to introduce a single wafer processing typeetching method into the line of mass production facilities, thetreatment time for one sheet has to be reduced. The level of thetreatment capability required for the cut sheet type thereof may bedecided through the designing of the entire semiconductor manufacturingprocess, but it is required, at least in order to make throughputmaximum, to make wafer passing between devices for treatment smoother sothat a retention time is made minimum. For that purpose, at least thesame level of treatment capability as that of a dry etching device isrequired.

The current single wafer processing dry etching process has thecapability of etching onto silicon oxide film having a thickness of 500nm to 1000 nm at around 25 to 30 sheets/hour. Accordingly, an etchingsolution having the capability of treatment at etching speeds in excessof 200 nm/min is required.

However, the conventional type of etching solution, of which etchingspeeds are required, dissolves and separates the resist at the sametime, and for this reason it is difficult to execute high-speedtreatment for a fine pattern on the insulating film.

Conventionally there exists no such etching solution where etchingtreatment can be effected onto a fine pattern with high speed.

An object of the present invention is to provide, under the situationdescribed above, an etching treatment agent which can etch an insulatingfilm with high speed without damaging the resist pattern.

Another object of the present invention is to provide an etchingsolution enabling treatment with realistic throughput when theinsulating film etching process in the semiconductor manufacturingprocess is replaced with the single wafer processing etching treatmentmethod.

Further, another object of the present invention is to provide anetching treatment liquid for preventing roughness on the surface of asemiconductor after etching.

SUMMARY OF THE INVENTION

According to the present invention an etchant is applied for the purposeof etching treatment onto insulating film with a resist as a mask formedon a substrate, containing 8 percent by weight through 19 percent byweight of hydrofluoric acid, 12 percent by weight through 42 percent byweight of ammonium fluoride, and a hydrogen ion concentration of10^(−6.0) through 10^(−1.8) mol/L. Preferably, the concentration of thehydrofluoric acid is set at 15 percent by weight through 19 percent byweight. An etchant according to the present invention is applied for thepurpose of etching onto silicon oxide film with a resist mask formed ona substrate with etching speeds to the silicon oxide film of 200 nm/minor more and a film-reduction rate of the resist of 50 nm/min or less.

Preferably added to the etchant according to the present invention is0.001 percent by weight through 1 percent by weight of a surfactant.

DETAILED DESCRIPTION OF THE INVENTION

The etching liquid according to the present invention contains 8 percentby weight through 19 percent by weight of HF, 12 percent by weightthrough 42 percent by weight of NH₄F, and a hydrogen ion concentrationof 10^(−6.0) through 10^(−1.8) mol/L.

When the concentration of HF, as well as, NH₄F is set within the rangedescribed above, the etching speeds, for example, of silicon thermaloxide film can be set to 200 nm/min or more by adjusting the temperaturein the etching solution. Also, by adjusting the hydrogen ionconcentration within a range from 10^(−6.0) through 10^(−1.8) mol/L, theresist separation during the etching treatment can be prevented, andalso a resist film-reduction speed can be suppressed to 50 nm/min orless. As a result, it is possible to minimize the error of dimensions ofa pattern on the insulating film due to the separation of as well as thethinner resist and to enhance uniformity on the wafer as a whole, sothat a high yielding rate of devices with higher performance can beachieved.

It should be noted that crystals may be precipitated in the etchingsolution depending on its composition; however, the etching solution maybe used by heating it up to dissolve the crystals. Also, etching speedscan be enhanced even more by heating the solution to a temperature of45° C. or less which will minimally affect the reduction of the resistfilm thickness. By setting the hydrofluoric acid concentration to 15percent by weight and heating the solution up to the temperature of 35°C. to 45° C. or more, extremely high-speed etching can be realized.

The etching solution according to the present invention can be preparedby mixing NH₄F solution, NH₄OH solution, or NH3 gas with HF solution ina specified ratio, and adding water or the like thereinto, to adjust theconcentration and pH.

The etching solution according to the present invention can easily beobtained by mixing, for example, a 50 percent by weight HF solution witha 50 percent by weight NH₄F solution so that HF will be 8 percent byweight through 19 percent by weight.

It is desirable to add a surfactant to the etching liquid according tothe present invention, and 0.001 percent by weight through 1 percent byweight thereof is preferably added therein. Addition of the surfactantin the liquid allows roughness on the surface of a semiconductor,exposed after removal of insulating film, to be suppressed. Further,when the pattern is finer, it is hard to wet the insulating film withetching liquid, causing etching uniformity to be reduced, but additionof the surfactant thereinto allows the wetting capability to beimproved, thus the etching uniformity is enhanced.

It should be noted that the effect described above is hardly obtainedwith-a rate of adding thereinto the surfactant of 0.001 percent byweight or less, and the same effect is obtained even with the rate of 1percent by weight or more.

As a surfactant, aliphatic amine (C_(n)H_(2n+1)NH₂; n=7 to 14),aliphatic carboxylic acid (C_(n)H_(2n+1)COOH; n=5 to 11), and aliphaticalcohol (C_(n)H_(2n+1)OH; n=6 to 12) are preferably applied. Thosehydrocarbon sections may be a straight chain or a structure havingbranches. And also, it is especially preferable that at least two typesamong those three types of surfactant are mixed and that any of thetypes is selected for application depending on the concentration of NH₄Fand HF.

The etching according to the present invention is treated as describedbelow as an example.

The etching solution, according to the present invention, is heated upto a specified temperature, if necessary, so that crystals are notprecipitated. The heated liquid is then sent to a nozzle, where it issupplied from the nozzle onto a rotating wafer. The etching solution issupplied while the nozzle is moved between the center and the peripheryof the wafer, so that the solution is supplied over the whole wafer.Also, the shift of the nozzle may be omitted by using a one-dimensionalnozzle having a length equal to the radius of the wafer.

Further, it is preferable that a megasonic-ultrasonic oscillator isprovided in the nozzle and that the etching liquid is supplied whileultrasonic waves in a range from 500 kHz to several MHz are irradiatedonto a wafer. With those operations, etching speeds are even moreincreased.

As resist treatment before etching is treated with the etching liquidaccording to the present invention, it is preferable to irradiateultraviolet rays onto a wafer after development of the resist, and thento subject the wafer to high-temperature baking. With those operations,a film reduction rate can be more suppressed, and finer treatment can beapplied with high uniformity.

As a condition of irradiation of ultraviolet rays, the wafer isirradiated with, for example, a UV lamp (220 nm to 320 nm) for 10 to 20minutes under the condition of 5 mW/cm² to 15 mW/cm².

Also, high-temperature baking is executed preferably in an N₂ or Ar gasatmosphere for 10 to 30 minutes at the temperature of 110° C. to 250° C.The baking temperature is more preferably 210° C. to 240° C.

The etching solution according to the present invention can be appliedfor etching on to insulating film such as silicon oxide films containingP, B, or As, oxide film such as tantalum oxide, and plasma siliconnitride film or the like in addition to silicon thermal oxidation film.

In embodiment one of the present invention, in order to make clear thedifference in effects of etching solution composition, etching wascarried out using a batch soaking method, and comparison was madebetween the etching speed and the resist film-reduction rate.

At first, thermal oxidation film was formed on a silicon wafer ofapproximately 1000 nm, and a photoresist was formed thereon of 1 μm. Itshould be noted that positive-type resists OFPR800 and TSMR8900 producedby Tokyo Oka were used for a resist.

The resists of various types of pattern having each width of 0.5 μm, 1μm, and 10 μm respectively were exposed to light, and developed, andthen subjected to post-bake treatment, for 30 minutes at the temperatureof 130° C. It should be noted that, for an etching solution having a pHof 2.4 or less, after the development, the resist was exposed byultraviolet rays (8W/cm²) for 15 minutes using a UV deuterium lamp, andhigh-temperature baking was executed to the resist in an N₂ atmospherefor 15 minutes at the temperature of 230° C.

This resist was soaked in etching solutions each having a differentcomposition and at a different temperature for 2 minutes, and an etchingspeed (nm/min) to silicon thermal oxide film and a resist film-reductionrate or the like were examined. Table 1 indicates the result. The resistfilm-reduction rates in Table 1 are obtained in relation to OFPR800, butsubstantially the same result was obtained with TSMR8900, so that TSMRis omitted herein. Peeling off the resist was herein observed with amicroscope, and a film-reduction rate was measured with an optical filmthickness gage.

It should be noted that each pH of the etching solution is measured atthe temperature of 35° C.

TABLE 1 Solution Etching temperature Composition 25° C. 35° C. 45° C. HFNH₄F Film- Film- Film- percent percent Etch reduction Etch reductionEtch reduction by by rate rate rate rate rate rate weight weight pH(nm/m) (nm) (nm/m) (nm) (nm/m) (nm)   5   0 <0.8  300 1000  483 1000 724 1000   5 20   3.6  950   0 1986   0  2958   0   7 15   2.4 1290   02235   0  3316   0   7 20   3.8 1380   0 2400   0  3613   0   7 35   4.41250   0 2256   0  3200   0   8   5 <0.8  960 1000 2012 1000  2850 1000  8 10   1.6 1460  100 2530 *300  3230 1000   8 12   1.8 1600  10 2780 10  4200  15   8 15   2.1 1750   0 3215   5  5360   5   8 35   4.2 1570  0 2750   0  4912   0   8 42   4.4 1420   0 2015   0  4570   0 10   0<0.8  666 1000 1094 1000  1608 1000 10   5 <0.8 1396 1000 2337 1000 3578 1000 10 10   1.0 1978 1000 3303 1000  5475 1000 10 15   1.8 2233  5 3872  10  6251  10 10   18.5   2.4 2251   0 3783   0  6200   0 10 20  3.2 2185   0 3818   0  6122   0 10 24   3.6 2100   0 3639   0  6146  0 10 28   3.8 1959   0 3407   0  6008   0 10 32   4.0 1810   0 3164  0  5294   0 10 40   5.0 1760   0 2516   0  4623   0 15 20 <0.8 37501000 6495 1000 10377 1000 15 24   1.8 3817   5 6381  10 10541  10 15 27  2.0 — 6350   5 10341   5 15   27.8   2.4 — 6258   0 10079   0 15 35  3.6 3026   0 5435   0  9315   0 18   26.3   1.7 — 7437 *300 12154  50018 30   1.9 — 7213   5 11960  10 18 31   2.0 — 7130   5 12030  10 19 20  0.9 4530 **500  7680  900 12690 1000 19 24   1.2 4732 *500 7980  70013340 1000 19 31   1.8 — 8016  10 13416  10 23 20 <0.8 5990 1000 10128 1000 15885 1000 25 20 <0.8 6510  100 11264  1000 17514 1000 25 25 <0.86420  100 10006  1000 15900 1000

In Table 1, any etchant without description of an etch rate indicates acase where crystals were precipitated at the corresponding temperature.Also, the sign (*) indicates a case where a 0.5 μm resist pattern waspeeled off, and the sign (**) indicates a case where a resist pattern of1.0 μm or less was peeled off. The film-reduction rate having 1000 nmindicates a case where the resist was completely dissolved.

As is evident from Table 1, it is found that the etchant according tothe present invention can realize high-speed etching, and in addition,the resist separation does not.occur, even on a fine pattern, and thefilm-reduction rate is extremely small.

In addition, in a case where the concentration of hydrofluoric acid isset to 15 percent by weight or more, etching can even more be speededup, an etching speed of 1 μm/min or more at the temperature of 45° C.can be obtained and also the resist film-reduction rate be suppressed,which provides support for the use of the etchant.

In embodiment two of the present invention, as a resist, a negative typeresist (OMR83) produced by Tokyo Oka was used, and similarly toembodiment one, separation of the resist and the film-reduction ratewere examined. Table 2 indicates the results. The film-reduction ratesare obtained at the liquid temperature of 45° C.

TABLE 2 Film-reduction HF concentration NH₄F concentration rate (nm) 100 1000 10 5 1000 10 10 1000 10 15 15 10 18.5 5 10 20 0 10 24 0 10 28 010 32 0

As shown in Table 2, substantially the same result as that of thepositive resist is obtained in the case of the negative resist, and forthis reason it is understood that the etching treatment agent accordingto the present invention also has less solubility to the negativeresist.

In embodiment three of the present invention, in order to examine aneffect of a surfactant, each silicon wafer was soaked in each of theetching solutions which were heated up to 35° C. for 10 minutes, andsurface roughness was examined for each silicon surface exposed whensilicon oxide film etched. Table 3 indicates the result.

Herein, as a surfactant the mixture of C₈H₁₇NH₂ and C₉H₁₉COOH in asequal molar ratio is added to each of the etching solutions in variousconcentrations. It should be noted that an atomic force microscope wasused for measurement of the surface roughness Ra.

TABLE 3 Surface Roughness HF concentration NH₄F concentration Addition(ppm) Ra (nm) 8 35 200 0.15 8 35 0 0.55 10 20 400 0.16 10 20 0 0.52 1520 400 0.17 15 20 0 0.49 18 30 300 0.16 18 30 0 0.55 19 31 300 0.17 1931 0 0.61

As is evident form Table 3, it is found that an initial value (0.15 to0.17 nm) for each surface roughness after the soaking can be maintainedby adding a surfactant to the etching solution, and that surfaceroughness can also be suppressed by the surfactant.

With an etching solution of the present invention, when etching isapplied onto oxide film on a surface of a silicon wafer with aphotoresist mask formed thereon, etching speeds onto the oxide film canbe achieved up to 200 nm/min or more at a temperature of 35° C. and to 1μm/min or more at the temperature of 45° C. depending on itscomposition.

As a result, although the time of around 300 minutes was required foretching by 500 nm onto 50 sheets of wafer in the out sheet method byusing the conventional type of 7:1-BHF, the time required for the sametreatment can be reduced to 30 minutes on condition that BHF as ahigh-speed etchant having etching speed of 1 μm/min while using atemperature of 45° C.

With this reduction, a shift of the etching process from the batchmethod based on the conventional technology to the cut sheet method canbe made quicker, and also uniformity within an etching-treated surfaceas well as a level of throughput based on the wet process each requiredby the manufacturing process of a semiconductor device can remarkably beimproved.

While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

What is claimed is:
 1. An etchant, comprising: a combination includinghydrofluoric acid of 15 percent by weight to 19 percent by weight andammonium fluoride of 12 percent by weight to 42 percent by weight, saidcombination having a hydrogen ion concentration of 10^(−6.0) mol/L to10^(−1.8) mol/L.
 2. The etchant as in claim 1 further comprising asurfactant of 0.001 percent by weight to 1 percent by weight.